As I suggested earlier in, no matter which type of backup medium you use, you should always keep multiple copies of your backups. That means multiple hard drives or multiple sets of removable media (of whichever sort). There's always the chance that a single backup will suffer the same fate as your hard drive: a random failure of some sort. If you attempt to restore files from a backup and find that it's damaged, you'll be grateful that you had a spare copy.
Better yet, if possible, consider maintaining three sets of backups, one of which is kept at a separate location from your computer at all times. I discuss off-site backups in more detail later under. Although an off-site backup is possible even if you have only two sets, having three makes it much more convenient.

Flash Drives

Flash drives, those small, solid-state, keychain-sized gizmos you plug into a USB port and use to shuttle files around, are all the rage these days. Because they're compact, have no moving parts, and can store, in some cases, as much data as three CDs, you may think they're a good backup medium. And for quick, one-off backups of files you're actively working on, they're not bad. At some hypothetical future date when you can buy, say, a 60 GB flash drive for little more than a hard drive, they may be useful for full backups too. For now, though, they are too small to store a complete, bootable Mac OS X system, and compared to any other medium available, the cost per gigabyte for archive backups is absurdly high.

SAN and NAS

Another trendy buzzword in data storage is SAN, or storage area network. A SAN is nothing more than one or more hard drives able to be shared among several computers, generally via high-speed FireWire, Fibre Channel, or SCSI connections (without using a conventional Ethernet-based network). NAS, or network attached storage, typically refers to one or more hard drives with their own Ethernet (or wireless) interfaces, sort of minimalist file servers. (Increasingly, they're simply called "network drives.") In other words, SAN and NAS equipment may be nearly identical, except for their interfaces.
Your office may have a SAN or NAS system available, and if enough adequate free space is available to you, there's nothing wrong with using either for backups. However, I would not buy SAN or NAS products primarily for home or small-office backup use. When it comes to backups, they provide little or no benefit over conventional FireWire or USB hard drives. And because they can't run backup software themselves, you still have to set up a backup serveror have each machine run its own backup application.

Local Network Servers

If, in your home or office, a computer is functioning as a file server, it's certainly worth considering whether you could use a network volume (AFP, SMB, or otherwise) as a backup destination.
In general, if you have control over the server yourself, I recommend adding a separate physical hard drive and installing client-server backup software. Otherwise, your backups will be commingled with other files, making it difficult to store them off-site and potentially creating a security risk.

If you do not personally have control over the server (i.e., if it's a shared company server), be circumspect about using it for backups. You could easily use up more space than you should, and you risk incurring the wrath of your IT manager. Even if she's willing to give you your own capacious partition on a server hard disk, you'll have much less flexibility and control over your data than if you backed it up to local media.

iDisk

Subscribers to Apple's .Mac service (at $100 per year) currently get up to 1 GB of iDisk storage space, with the option to increase to 2 GB for $50 per year or 4 GB for $100 per year. Apple's Backup application, and most other backup utilities, can use an iDisk as a backup destination. Unfortunately, even 2 GB is far too little space to meet most users' needs, and transfer speeds to the .Mac servers are often quite slow, even for users with broadband connections. In addition, you cannot make a bootable backup onto an iDisk. For these reasons, your iDisk is not an ideal backup destination.
On the other hand, for casual (manual or automatic) backups of just a few files between regularly scheduled archives, an iDisk does make a convenientand inherently off-sitedestination.

Internet Backup Services

A few years ago, during the dot-com boom, Internet backup services were hailed as the next big thing. The idea is simple: using either a conventional backup program such as Retrospect or proprietary software, perform backups as usual, but use secure Internet file serversrather than local or network volumesas the destination. In other words, an Internet backup service is basically a more-sophisticated version of using Apple Backup with your iDisk.
In theory, I like the idea of remote Internet backup. In fact, I used such a service for a whileuntil it went out of business. The problem was that the cost of doing this type of business was out of proportion to the amount of money most consumers could be expected to pay.
Only a handful of Mac-compatible Internet backup services remain, and they are still quite pricey, especially compared to the cost of purchasing your own hard drives. Here are the ones I'm aware of:

• BackJack: BackJack (www.backjack.com) charges $12.50 per month for 2 GB of storage space, with additional space available at $2.75 per gigabyte (the per-gigabyte cost decreases as you add storage). An alternate plan, which includes extra, redundant backups, costs $17.50 per month for 2 GB and $6.00 per additional gigabyte (again, with cost reductions as you add storage).
• Tuloy: Tuloy (www.tuloy.com) charges $3.95 per month for 500 MB of storage, their maximum.
• Prolifix: Prolifix (www.prolifix.net) uses cross-platform, Java-based software. The company charges $9.95 per month for 500 MB of storage and $28.95 per month for 8 GB, with intermediate levels available. (Contact Prolifix for quotes on higher storage quotas.)
• Datatrieve: Located in the U.K., Datatrieve uses a Java-based client (www.datatrieve.co.uk). They charge £5 (about $9) per month for 1 GB of storage, and £64 (about $112) per month for 20 GB. As with Prolifix, intermediate levels and higher storage quotas are also available.

All these services are constrained by the uplink bandwidth of your Internet connection, and none can make bootable duplicates.

Note
All these services except Tuloy also compress your data, so you may be able to fit much more on their servers than the amounts listed.

On the plus side, Internet backup services keep your files safely off-site with absolutely no effort on your partand they do so for every backup, not merely on a weekly (or "whenever-I-remember") basis. BackJack, Prolifix, and Datatrieve also encrypt your files (unlike Apple Backup) and make their own redundant, off-site copies of your data (though BackJack charges extra for redundant backups). If, despite my repeated encouragements, you are unable or unwilling to store a set of backup media outside your home or office, an Internet backup service can make that process painless. Even if you do maintain diligent off-site backups, an Internet backup service can provide extra insurance for particularly important files.
These services are no substitute for duplicates. As for archives, unless you have an unusually small home folder, you'll probably find the cost of archiving all your personal files over the Internet prohibitive. But, if you can afford it, an Internet backup service may make a reasonable supplement to conventional duplicates and archives, especially for files you're actively working on. Although these services excel in security and ease of use, you must carefully choose which files to include (or exclude) to avoid incurring extremely large bills.

Camcorders

Say you can't afford to buy two or three hard drives. On the other hand, you find optical media too limited in capacity. Then you hear about an amazing product called DV Backup (www.coolatoola.com). This software enables you to use your FireWire-enabled digital camcorder as a backup device. Because MiniDV or Hi8 tapes are relatively inexpensive and easily reusable, media cost is reasonablebut more importantly, you avoid the expense of conventional tape drives by pressing into service a device you already own. Best of all, a single 60-minute tape can store as much as 16.5 GB of data, and larger backups can span multiple tapes. You may think this is the ideal solutionwhat's not to like?

Amazon S3

Amazon.com recently introduced a service called S3, which provides virtually limitlessyet inexpensiveonline storage, complete with encrypted transfer. Could this be the Internet backup solution we've all been waiting for? Maybe in the future, but at the moment, some significant issues exist.
To sign up for Amazon S3, fill out a form (including credit card information) at www.amazon.com/s3/. After your account is activated, Amazon.com provides you with two access keys, both of which you'll need to reach your space on their servers. You can store as much data as you want for $0.15 per gigabyte per month, plus $0.20 per gigabyte transferred (upload or download)a tiny fraction of what you'd pay for a service like BackJack.
You should be aware of a couple of catches, though. First, you need an application that knows how to communicate with the S3 service, because ordinary FTP, Web, and backup clients cannot. As I write this, the only mainstream Mac Internet client with built-in S3 support is Interarchy (www.interarchy.com; $39). However, a new, free tool called JungleDisk (www.jungledisk.com) performs some magic to mount your S3 storage space as a network volume. JungleDisk handles the back-end communication with S3 and runs a WebDAV server in the background on your local machine; you then connect to that WebDAV server using the Finder's Go > Connect to Server command to access your files.
Because most backup programs can copy files to any mounted volume, they should also be able to work with Amazon S3 via JungleDisk, right? Well, maybe. A second catch is that no single file on S3 can be larger than 5 GB. This spells trouble for most archiving schemes (which often produce files or disk images larger than 5 GB). And without using archiving software, you're likely to lose important metadata when copying files. In addition, I've found early versions of JungleDisk to be somewhat finicky; I ran into difficulties getting the virtual network volume to mount and unmount at the right times.
For now, these and other problems limit S3's usefulness for backups. But when full-featured backup programs gain direct support for S3, I expect it'll turn into a fantastic and cost-effective backup option.
I have rather mixed feelings about using a camcorder as a backup device. Well, not truly mixed: I wouldn't do it myself. All right, if I were stuck on a desert island with just my PowerBook and a camcorder, then maybe; as I mentioned earlier, I believe that something is better than nothing. But for regular, day-to-day use, I worry that your camcorder may actually be worse than nothing.
With all due respect to author Tim Hewett, who has done what can only be called an extraordinary engineering job, DV Backup is at the mercy of your camcorder and tapes, which were not engineered to provide the bit-perfect quality you need for backups. DV Backup, to its credit, does provide user-adjustable error correction as well as an optional data verification pass after recording your data. However, you trade security for speed and capacity; at the highest level of error correction, which essentially puts two copies of each data block on the tape, backups take twice as long as without (logically enough) and use up twice the tape. Because magnetic tape is notoriously error-prone, I wouldn't recommend using anything less than the highest level of protection. But doing so significantly reduces the advantages of this approach.
Here are some other reasons I urge you to think twice before trusting your backups to your camcorder:

• The speed of backups and restoration is much slower even than that of optical media, and nowhere near the speed of hard drives.
• Restoring arbitrary individual files is possible (though time-consuming) only if you store your data uncompressed.
• Your computer monopolizes your camcorder. If you want to shoot video, you have to go without backups for a while (and vice-versa).
• Because digital camcorders were not designed for data backup, the (often miniature) electronics may wear out prematurely due to the frequent stops and starts imposed by backup software.

If you still think a camcorder backup is right for you, you can minimize your risks by observing the following advice:

• Buy high-quality tapes, and use only brand-new tapes for backups. And always stick with the same brand of tape for best results.
• Use the SP speed rather than the LP speed.
• Always use the highest level of error correction; always select the auto-verify option; never use compression.
• Perform test restorations of your data on a regular basis.
• Consider supplementing your camcorder with a secondary backup method, such as periodic backups to optical media.

Hardware Recommendations

I strongly believe that decisions about hardware should not be made on price alone. You may find the cost per gigabyte of storage to be only $0.15 for DVD-R, for example, versus $1.00 for a hard drivebut that's only part of the story. Speed, convenience, flexibility, and the ability to make bootable backups all add tremendous value to hard drives. Even if you can afford only one external hard drive, making it part of your backup system will pay for itself many times over in saved time and aggravation. If your budget permits, two or even three moderately large external hard drives are definitely the way to go.
That said, if you're looking purely for the most economical hardware path, use your built-in SuperDrive and record backups onto DVD-RW media. Your hardware cost is zero, and $50 should buy you enough blank media to last years.
The Iomega REV comes much closer to the sweet spot at the intersection of capacity, speed, and affordability than optical, magneto-optical, or digital tape media, not to mention Zip and Jaz drives. Assuming REV turns out to be reasonably reliable, it's not a bad choice, but I recommend it only if you can comfortably fit a complete duplicate of your main startup volume within the 35 GB limit of a single REV disk.